Locks are widely used to guard articles that have obvious or potential security concerns. For instance, a padlock may be used to lock the zipper of a piece of luggage to prevent unauthorized opening.
Due to security reasons, nowadays airports have very strict standards for luggage security inspection. With luggage that may be a security risk, mandatory opening of the luggage for security inspection could take place. For the luggage that has been locked, the lock has to be broken. After security inspection, the lock is damaged and becomes unusable. As a result, the damaged lock can no longer provide protection after the security inspection has been completed.
To remedy the problem of lock damage during security inspection, a lock equipped with two locking units has been developed. For instance, Travel Sentry™ Co. of U.S.A. introduced a number of locks for this purpose. They mainly have one locking unit to allow luggage owners to lock and unlock during use, and another locking unit for security inspection. Hence the security inspection people can perform routine security inspection through a normal unlocking procedure to open the lock, and close the lock after the security inspection is finished. Therefore damage of the lock may be prevented, and the luggage has proper protection after security inspection.
However, the lock mentioned above still has a drawback, namely that after the security inspection was done and the lock is relocked again, there is no indication to warn the luggage owners that the lock has been unlocked.